A drive method using an inverter has been employed for performing drive control of an AC motor with a DC power supply. For example, in a motor vehicle such as an electric vehicle, a hybrid vehicle, a fuel-cell electric vehicle or the like, the inverter generally controls an output torque of an AC motor employed for vehicle running. Typically, the AC motor is supplied with a voltage switched by the inverter according to the PWM control that is based on a comparison between voltages of a voltage command and a carrier.
In connection with the control of the AC motor, for example, Japanese Patent Laying-Open No. 2000-324842 (Patent Document 1) has disclosed a control device of an electric power converting device. This control device includes a reference voltage generator that performs AC/DC conversion of a power by controlling on/off of a plurality of switching elements according to a control signal and thereby provides a reference voltage, a carrier generator that provides a saw-tooth carrier having a frequency sufficiently higher than that of an AC output or an AC input, a comparator that provides a PWM signal controlling on/off of the plurality of switching elements by comparing levels of the reference voltage and the saw-tooth carrier with each other, and a correction signal generator generating a correction signal that exhibits a symmetrical wave with respect to the frequency of the AC output or input.
In the patent literature 1, a correction signal corrects the saw-tooth carrier of the carrier generator to provide a corrected carrier that is a symmetrical wave with respect to the frequency of the AC output or AC input, and this corrected carrier corrects the PWM signal provided from the comparator. Thereby, the PWM signal is corrected to form the symmetrical wave with respect to the frequency of the AC output or AC input, and the corrected PWM signal does not include a low-order harmonic of the even-numbered order so that it is possible to reduce a distortion of the waveform of the AC output or AC input due to the low-order harmonic.